The present invention relates to a rotary vane pump for delivering a fluid, and which includes a delivery device accommodated in a housing, a feed channel for the fluid which is formed in the housing, and which extends in the suction region of the delivery device, and terminates in a jet chamber upstream thereof, and with an injector device, which is used to deliver the fluid, which discharges with a jet nozzle into a jet chamber. In so doing, the jet nozzle injects the fluid under a high pressure into the fluid entering the jet chamber from the feed channel, thereby entraining or accelerating it, with the jet chamber being hydraulically connected via a suction channel to at least two suction chambers of the delivery device.
Pumps of the kind under discussion, for example vane cell pumps are known from practice, for example, from U.S. Pat. Nos. 5,496,152 and 4,971,525, and DE 41 22 433 C2.
Pumps of the described type are used, for example, in steering boosters, and they deliver a special oil to provide assistance to the steering force that is to be applied to the steering wheel of an automobile. Preferably, the pumps are vane cell pumps, which take in oil from a reservoir outside of the pump, for example, an external tank. Such pumps are normally equipped with a flow control valve, which permits delivering the oil from the high-pressure region to the intake region of the pump. Effective a certain pump speed, and with a constantly adjustable flow rate, the flow control valve opens a discharge bore, through which the oil under a high pressure is able to leave. The oil enters the intake area of the delivery device.
U.S. Pat. No. 5,496,152 discloses a pump of the described type, which comprises for realizing as much as possible an operation free from cavitations, a very special delivery system for delivering the tank oil. Specifically, an injector device is provided that operates in a manner similar to that of a water jet pump. The injector device is biased by a fluid flowing at a high velocity, which is supplied to the injector device from the high-pressure area, preferably via a flow control valve. The injector device injects this high velocity fluid into the fluid leaving the feed channel in the area of a jet chamber upstream of the delivery device. As a result, the fluid coming from the tank is entrained or accelerated. From there, it enters the intake area of the delivery device via a further channel system.
The technology disclosed in the '152 patent and relating to the use of an injector device, however, is problematic, inasmuch as the disclosed injector device operates with a jet nozzle only on one side of the housing, and must deliver from there the fluid coming from the tank to both sides of the housing, i.e., into the respective intake regions, to make the fluid available to an adequate extent on both sides of the housing to the suction chambers associated on both sides of the delivery device or rotational group.
The main problem underlying the prior art may be seen in that the valve jet that flows off on the valve piston at a high velocity into the jet nozzle, preferably upstream of the valve piston under a high pressure, if need be, extends basically obliquely, and that symmetrically configured channels are therefore unsuitable.
Because of the normally different supply of jets to the suction chambers arranged on both sides, different pressure conditions occur in the fluid, which in turn leads to a different loading of the suction chambers on both sides. In particular, in the case of high flow rates of the pump, this will lead to cavitation or to damage resulting from cavitation. Furthermore, an even filling of the intake areas on both sides becomes questionable.
At any rate, the prior art does not ensure that the suction chambers are uniformly filled. Quite the contrary, pressure conditions and flow velocities of the fluid, which prevail upstream of the suction chambers, lead to a different filling, which in turn causes the foregoing problems, i.e., cavitation and also noise in the pump.
It is therefore an object of the present invention to improve and further develop a pump of the described type in such a manner that cavitation and noise in the pump are essentially avoided with simple constructional means.